This invention relates to mobile radio communications systems and, more particularly, to a method and apparatus for controlling their operation near sensitive areas.
A significant problem with mobile radio communications systems is the potentially harmful interference they may cause to other electronic equipment. As the use of mobile radios becomes more widespread, the occurrence of this interference will become more frequent. The problem is usually caused by the close proximity of the mobile radio transmitter to another piece of electronic equipment and the sensitivity of that equipment to extraneous radio signals.
There are two places where this problem is particularly dangerous, and perhaps life-threatening. These are in hospitals and in aircraft. As electronic control systems pervade other environments, however, the areas of danger will increase. Interference to automobile electronic braking systems, airbag actuators, or train system controls are examples of the areas where radio interference must be prevented to preserve the safety of operators and passengers.
Presently, the method used to prevent interference of this sort is simply to prohibit the use of mobile radios in sensitive areas. Passengers on aircraft are routinely told not to use their cellular phones. Doctors and staff are routinely told not to bring their cellular phones into some areas of the hospital. Unfortunately not everyone understands the danger and some operate their phones anyway. Some people use their cellular phones in aircraft. Even some radio engineers have said that because they know the aircraft radio frequencies are not the same as the cellular phone frequencies, there can be no interference and thus they are justified in using their mobile phone. They do not understand that interference between electronic systems may occur even when the systems operate in separate radio bands. As well, few people understand that even if they are not talking on the phone, if the phone is in xe2x80x9cstandbyxe2x80x9d mode, it may be still active and occasionally transmitting on the signalling channels and thus may still be a potential source of interference. As more and more people carry and use mobile phones, there will be more and more operation of these phones in areas where they are nominally prohibited.
In addition, as mobile radio systems are increasingly used for data communications, either through mobile radio systems or separate radio data services, many people will be operating these systems in prohibited areas not realizing that the warning not to operate their cellular phone also applies to their mobile radio fax modem or data service. Many laptop computers with radio modems are operated on aircraft and, therefore, there is a potential that these will interfere with the electronic aircraft equipment.
An effective means to limit the possibility of interference is to reduce the mobile radio transmit power. Several of the radio standards do provide low power modes of operation. If the mobile radio is commanded, via the signalling channels, to operate in the low power modes, their operation may be safe in some areas. Further, the signalling channels may also be used to broadcast (at low power) a message to the mobile handset which prohibits the handset from operation in areas where no level of mobile emissions can be tolerated. Thus the combination of low power operation and appropriate signalling commands can provide a means to protect sensitive areas from mobile radio interference.
New mobile radio systems are currently being developed by the Third Generation Partnership Program (3GPP), a global consortium of national standards associations. Among these are the UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access Network, commonly known as the UTRAN, and the CDMA2000, a new third generation system which makes use of Code Division Multiple Access (CDMA). Along with the development of these new mobile radio systems, new capabilities are being introduced that can be used to better facilitate the control of interference in protected regions.
One of the features being introduced in the new radio systems is a xe2x80x9clocation findingxe2x80x9d service whereby the geographic location of the mobile radio can be determined. Measurements may be made of the signals transmitted as part of the normal operation of the mobile radio system, or they may be made of signals specifically transmitted for this purpose (for example, global satellite navigation systems such as the Global Positioning System (GPS) provided by the United States Department of Defense). Calculations are then made using these radio signal measurements to determine the spatial location of the mobile radio receiver.
To prevent undesirable radio transmissions there have been proposed several mobile communications systems and mobile terminals having a capability of inhibiting radio transmission. One proposed method of preventing mobile radio transmissions in prohibited areas is described in UK Patent Application GB 2,325,592 published on Nov. 25, 1998, wherein a mobile radio calculates its location based upon radio signals received from at least three surrounding base stations. The mobile stores a plurality of transmission inhibition areas and the transceiver is controlled depending on the location of the mobile radio with respect to the stored inhibition areas. One disadvantage of the above technique is that the prohibited areas must be programmed into the mobile radio and are, thus, not easily adaptable to change. A portion of memory must also be reserved to store these protected areas. Secondly, the location calculation is done within the mobile using downlink radio control signals received from at least three different base stations. This imposes obvious constrains on network configuration.
Another method described in U.S. application Ser. No. 08/957,025 filed on Oct. 24, 1997, proposes a system whereby mobile radios are provided with a low power mode of operation and are commanded, via their signalling channels, to operate in the low power mode when within range of a low power signal from a base station within a protected area. In areas where it may be undesirable to have any radio transmissions, even at low power levels, the base station may broadcast an inhibiting signal which will instruct the mobile not to operate its transmitter while in the area. In this method, the protected region is defined by the region where these inhibiting transmissions can be received. The base stations, in this case, are restricted to specific locations needed to shape the transmission coverage areas to match the protected regions.
Devices, commonly known as jammers, are also sometimes used to block the operation of cellular phones. These devices inhibit operation by transmitting radio power that jams or disrupts the signalling channels of the mobile phone system and thereby prevent the mobiles from operating. Although all incoming and outgoing calls are blocked, these systems do not protect against interference to sensitive equipment as the radio jamming signal must be quite strong to assure it overpowers regular transmissions of the mobile radio system.
There is also another level of interference caused, not by the mobile radios themselves, but by the activities of their users. A common example of this is the ringing of mobile phones in meetings. This is, at best, a minor annoyance but at other times can be a serious disruption as many meeting delegates fumble with their phones to determine if the call is for them. It is especially annoying if people answer and talk on the phone disturbing others in the room. Many restaurants and concert halls prohibit carrying mobile phones for precisely this reason. This is, perhaps, not quite as life threatening as previous examples, but nonetheless is a serious public nuisance.
Because it is impossible to prevent people from operating mobile radio equipment (e.g. cellular phones or radio fax modems in portable computers) in sensitive areas, the present invention provides an arrangement whereby they can be operated safely in these areas, or the mobile radio can be disabled if the area cannot tolerate any level of mobile emissions.
The present invention provides a new technique for controlling the operation of mobile radios in protected regions by making use of the new xe2x80x9clocation findingxe2x80x9d service capability of the mobile network. It also proposes using broadcast control signals to indicate the type of mobile radio operation (e.g. no audible ringing or outgoing calls only) permitted in the restricted region. The present invention operates in the following way:
(a) A base station with coverage in the sensitive area is installed and operated at a power level such as to be below the level of susceptibility of the sensitive equipment in the area. This base station may be an existing installed base station with suitable coverage and power level.
(b) The base station providing coverage in the sensitive area transmits information on protected region boundaries and conditions of restricted operation (using the mobile radio system broadcast control channels and the signalling mechanisms in the air interface standard).
(c) The mobile radio operation is controlled such that, before it makes any transmissions, it receives and interprets the local broadcast control channels.
(d) The mobile radio makes use of a suitable xe2x80x9clocation findingxe2x80x9d technique to determine its location.
(e) The mobile radio compares its measured location to the protected region boundaries to determine whether or not it is inside a protected region and thus, needs to constrain its operation.
(f) If the mobile radio is within a protected region, it constrains its operation according to the conditions broadcast for that protected region (e.g. low power operation or no audible ringing).
(g) If the mobile radio is not within a protected region, then it operates in the normal (unconstrained) manner.
The notion of a protected region is extended from one which involves just the mobile radio transmitter power to one where mode of use of the mobile is also controlled. Control of operation may include no audible ringing, outgoing calls only, no transmissions at all, low power mode of operation or any other conceivable means to protect against interference and ensure that social etiquette is maintained.
Manufacturers of mobile radio products are often asked how and if it is safe to operate them in sensitive areas. By means of the present invention to assure controlled operation through the use of a suitable xe2x80x9clocation finding techniquexe2x80x9d and interpretation of broadcast control messages (decoding of protected region coordinates), radio communication systems can be provided with the possibility of interference in sensitive areas being minimised.
The use of mobile radios is widespread, but they are prohibited in hospitals and aircraft, for example. If an extension to the signalling protocols of the relevant standards is made providing for controlled operation of mobile radio equipment according to the present invention, then the equipment may be used in more areas and without the danger of inadvertent interference because someone forgot or ignored a request to turn off their radio equipment. An additional advantage is that, unlike jammers, the invention uses signalling to restrict operation thereby providing a platform where all calls except emergency calls can be blocked. This is highly desirable as it would assure access to emergency services at all times.
In addition to a new method, the invention also relates to a new base station, a new mobile radio unit and a new mobile communication system including the new base station and mobile radio unit.